Influence of Course Type on Upper Body Muscle Activity in Elite Cross

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provided by CLoK J Sci Cycling. Vol. 1(2), 2-9

RESEARCH ARTICLE Open Access

Influence of course type on upper body muscle activity in elite Cross-Country and Downhill mountain bikers during off Road Downhill Cycling Howard T Hurst1, Mikael Swarén2, 3, Kim Hébert-Losier2, Fredrik Ericsson4, Jonathan Sinclair1, Stephen Atkins1 and Hans-Christer Holmberg2, 5

Abstract This study aimed to investigate upper body muscle activity using surface electromyography (sEMG) in elite cross- country (XCO) and downhill (DH) cyclists during off road descending and the influence of man-made (MM) and natural terrain (NT) descents on muscle activity. Twelve male elite mountain bikers (n=6 XCO; age 23 ± 4 yrs; stature 180.5 ± 5.6 cm; body mass 70.0 ± 6.4 kg and n=6 DH; age 20 ± 2 yrs; stature 178.8 ± 3.1 cm; body mass 75.0 ± 3.0 kg) took part in this study. sEMG were recorded from the left biceps brachii, triceps brachii, latissimus dorsi and brachioradialis muscles and expressed as a percentage of maximal voluntary isometric contraction (% MVIC). Both groups performed single runs on different MM and NT courses specific to their cycling modality. Significant differences in mean % MVIC were found between biceps brachii and triceps brachii (p=.016) and triceps brachii and latissimus dorsi (p=.046) during MM descents and between biceps brachii and triceps brachii (p=.008) and triceps brachii and latissimus dorsi (p=.031) during NT descents within the DH group. Significant differences in mean % MVIC were found between biceps brachii and brachioradialis (p=.022) for MM runs and between biceps brachii and brachioradialis (p=.013) for NT runs within the XCO group. Upper body muscle activity differs according to the type of downhill terrain, and appears to be specific to DH and XCO riders. Therefore, the discipline specific impact on muscle activation and the type of course terrain ridden should be considered when mountain bikers

engage in upper body conditioning programmes.

Keywords: cycling, mountain biking, downhill, surface EMG, performance.

 Contact email: [email protected] (HT. Hurst) skill, whilst elite XCO races last approximately 1.5- 1.75 hrs, are competed over laps of between 4-6 km in 1 University of Central Lancashire, Preston, United Kingdom length, and focus more on aerobic fitness (Union Cycliste Internationale, 2012). 2 Swedish Winter Sports Research Centre, Mid Sweden University, Östersund, Sweden Both specialist downhill courses and downhill sections of XCO courses can be classified as either natural (NT) 3 Royal Institute of Technology, Stockholm, Sweden or man-made (MM). Natural courses rely 4 Swedish Cycling Federation, Stockholm, Sweden predominately on the geography and existing obstacles

5 to provide a technical challenge; whilst MM courses Swedish Olympic Committee, Stockholm, Sweden ______are created using machinery to sculpt a track down the hillside that generally includes machine-built jumps Received: 4 July 2012. Accepted: 20 November 2012. and numerous smooth banked corners. Generally, MM courses also tend to be faster than NT courses due to Introduction the less rugged nature of these courses. The skills Mountain biking (MTB) is composed of several sub- required to ride MM and NT courses differ, and riders disciplines, with Olympic Cross-Country (XCO) and will usually change their body position on the bike in Downhill (DH) being the most popular. Both XCO and response to the type of terrain. Therefore, course type DH can be characterised as high intensity, intermittent may influence muscle activity during downhill cycling. activities that require riders to compete over varied Elite XCO and DH cyclists generally compete in terrain, including rocky paths, technical single-track approximately twenty to thirty races per season with and open forestry roads; and also include frequent races often comprised of qualification rounds and a obstacles, such as jumps and vertical drops (Lee et al. final (Sperlich et al. 2012). As a result cyclists are 2002). Typically, elite DH races last between 2-5 min required to perform a high volume of downhill riding, and 1.5-3.5 km with the emphasis being on technical both during the course of a weekend race and throughout the season, irrespective of discipline.

© 2012 Hurst; licensee JSC. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Hurst et al. (2012). Influence of course type on upper body muscle activity in elite Cross-Country and Downhill mountain bikers during off Road Downhill Cycling. Journal of Science and Cycling, 1(2): 2-9

However, modern XCO and DH bicycles differ given course. In addition, such knowledge may also considerably, with DH bicycles having between 200- lead to more effective training plans to aid MTB 230 mm of front and rear suspension travel, whilst performance and potentially reduce the risks of injury XCO bicycles have between 80-100 mm of suspension through improved bicycle handling and reduced muscle travel that can be front and rear or front only. These fatigue. specificities in bicycle designs may lead to different The aims of this study were therefore to 1) quantify upper body muscle activity in DH and XCO riders most upper body muscle activity during off road downhill likely linked to differences in force transmission to the cycling in elite XCO and DH cyclists and 2) investigate upper body and differing body positions on the the influence of course type on upper body muscle bicycles. activity. Whilst there is a plethora of research pertaining to the aerobic and anaerobic characteristics of XCO racing, Materials and methods with comparisons often made to road cycling (Wilber et Participants al. 1997; Stapelfeldt et al. 2004; Impellizzeri et al. Ethical approval for the study was granted by the 2005; Prins et al. 2007), there is a clear paucity of data University of Central Lancashire Ethics Committee and on the performance characteristics of elite DH the Swedish Winter Sports Research Centre and the mountain bikers. research proposal was in accordance with the Currently, the only study to use elite level DH cyclists Declaration of Helsinki. Participants were informed is Sperlich et al. (2012), who investigated the psycho- both verbally and in writing of the test procedures and physiological stresses of DH racing. Hurst and Atkins written informed consent was obtained. Twelve male (2006) investigated the power, cadence and heart rate elite mountain bikers (n=6 XCO; age 23 ± 4 yrs; stature responses to DH riding; however, their study used well 180.5 ± 5.6 cm; body mass 70.0 ± 6.4 kg and n=6 DH; trained amateur DH cyclists and not elite athletes. age 20 ± 2 yrs; stature 178.8 ± 3.1 cm; body mass 75.0 Despite significant fluctuations in power and cadence, ± 3.0 kg) took part in this study. All riders represented Hurst and Atkins (2006) reported remarkably stable the Swedish National Cycling team at their respective heart rates during downhill riding. They concluded that disciplines. No significant differences were found for this, in part, may be due to the influence of isometric anthropometric variables, with the exception of contractions of the upper body musculature. However, percentage body fat (11.2 ± 4.1 % and 5.6 ± 1.3 %; the recruitment activity of these muscles has yet to be p=0.010, for DH and XCO respectively). quantified during downhill mountain biking in elite Anthropometric measures were conducted following XCO and DH riders. the guidelines of Lohman et al. (1989) and using the Several studies have used surface electromyography seven site prediction equation of Jackson and Pollock (sEMG) to investigate the activity of muscles in (1978). response to different road cycling conditions (Egaña et al. 2010; Matsuura et al. 2011; Blake et al. 2012), Course Profile though these studies were generally laboratory based Testing was conducted at the Åre Bike Park, Åre, and focused primarily on the lower limb muscles. Duc Sweden. All participants were allowed to use their own et al. (2008) investigated the influence of hand grip race bicycles, with XCO riders using hard-tail XCO position during uphill road cycling on upper body mountain bikes with between 100 ± 0 mm of front only muscle activity. However, this was again laboratory suspension travel, whilst DH riders used full- based and the hand grip positions used in road cycling suspension DH bikes with 202 ± 1.55 mm of do not reflect those used in MTB. Therefore, the suspension travel. Suspension systems were set up muscle activity observed in MTB are likely to differ according to individual preferences with respect to from those observed in road cycling. To our compression rate and rebound dampening. Each group knowledge, Hurst et al. (2011) is the only study to were tested on two different courses, technically investigate upper body muscle activity during relevant to their discipline. Courses were categorised as simulated MTB. However, the study was limited in that either NT XCO (length = 1358 m, vertical drop = 271 it was also performed within a laboratory setting, m, mean gradient = 19.7 %) and NT DH (length = 1363 simulated a single drop of only 30 cm and recruited non m, vertical drop = 431 m, mean gradient = 29.2 %) or cyclists as participants. As such, the results of their MM XCO (length = 1387 m, vertical drop = 273 m, study may not compare, or be generalised, to the mean gradient = 19.5 %) and MM DH (length = 2182 responses of elite level athletes in a field-based m, vertical drop = 473 m, mean gradient = 22.9 %). environment. Courses were representative of the type of terrain The quantification of upper body muscle activity encountered during downhill sections of XCO courses during downhill off road cycling has practical and DH specific tracks at a World Cup level. Riders implications for riders and coaches. Unlike road-based were allowed two days to familiarise themselves with cycling disciplines, MTB involves more dynamic the courses prior to testing. Course length and profiles movements of the upper body to manoeuvre the bicycle were recorded using a 5 Hz global positioning satellite over and around obstacles and to aid the dampening of system (GPS) (Minimax X3, Catapult, Australia) trail shocks. Knowledge of this activity may help riders positioned in a harness at approximately the C7 and coaches to set up bicycles more effectively for a vertebrae. The GPS system was also used to record mean and peak velocity.

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position to indicate the start of each run. The change in As no direct comparisons between groups were planned elbow joint angle was indicative of riders pulling on the at onset of the study, the use of different MM and NT handlebars during acceleration off the start line. Run courses for each group is justified considering that the times were recorded using a Freelap TX Junior wireless primary aims of the study were to quantify upper body radio transmitter system (Freelap, Switzerland). During muscle activity in XCO and DH riders and investigate post processing data were full-wave rectified then the influence of course type on muscle activity within filtered at 20 Hz using a first order low pass zero-lag groups. From a health and safety perspective, it was Butterworth filter in accordance with Li and Caldwell deemed unsafe to require XCO riders to complete the (1998 and 1999) to create a linear envelope. Mean and same MM and NT courses as the DH riders due to the peak sEMG amplitudes were determined for each differences in bicycle designs outlined above. In muscle and run using DataLink Version 5.06 addition, the use of different courses was more (Biometrics Ltd., UK). ecologically valid as the technical demands A maximal voluntary isometric contractions (MVIC) experienced during racing differ between groups. was performed for each muscle prior to data collection on course. Due to the field-based nature of testing and Surface EMG Processing and Analysis in the absence of fixed immovable objects against Surface electromyography (sEMG) data were recorded which to perform MVIC’s, participants performed them using Biometrics Bipolar AG-AgCl differential sEMG against the resistance of an examiner following the sensors (model SX230, Biometrics Ltd., UK) at 1000 clinical recommendations of Kendall et al. (2005) for Hz from the left biceps brachii, triceps brachii, manual muscle testing. In order to minimise variability latissimus dorsi and brachioradialis muscles. The upper the same examiner performed all assessments of body movement patterns used to absorb trail shock in MVIC. Biceps brachii, triceps brachii and mountain biking are similar to those observed during brachioradialis MVIC’s were performed in a seated push up exercises, and hence the above muscles were position with the left elbow in a 90° position. selected for investigation as they are the primary Participants were instructed to keep the elbow in muscles involved during push ups (Freeman et al., contact with the side of the torso during the MVIC’s, to 2006). The left side of the body was chosen due to this reduce extraneous movements, whilst the examiner being the side of the dominant braking hand. Sensors provided a manual resistance to oppose the prime were positioned longitudinally in parallel to the muscle movement of the muscle under investigation. The fibres on the medial aspect of each muscle. Positioning MVIC’s for latissimus dorsi were performed with the of the sensors was in accordance with the Surface EMG participants’ lying prone with the shoulder blades for Non-Invasive Assessment of Muscles project retracted and the arm in adduction, extension, and (SENIAM) recommendations. Prior to placement of the internal rotation whilst attempting to raise the left arm sensors, the skin was prepared by shaving the area, posteriorly against the manual resistance of the lightly abrading and cleaning with alcohol wipes to examiner. minimise skin impedance and electrode-to-skin Due to the use of manual resistance for the artefacts. A ground reference cable (R306) was placed determination of MVIC’s, angular joint displacement on the styloid process of the right radius to reduce the of the elbow and shoulder was a possibility. Though likelihood of 50 Hz noise. In addition, a pre-calibrated this was not formally assessed during the performance (absolute zero) twin axis goniometer (model SG110, of MVICs, it was not observed. Nonetheless, to account Biometrics Ltd., UK) was used to record elbow joint for the possible influence of joint displacement and in angle in the sagittal plane. This was placed across the accordance to standard MVIC data collection left elbow joint ensuring that the goniometer crossed procedures for sEMG normalization, three trials for the joint centre. Elbow joint angle was defined as a each muscle were performed. Maximal voluntary relative angle, with 0° indicating full extension and isometric contraction values for each muscle 180° indicating full flexion. All sensors were secured in represented 100 % and with the highest value place using medical tape and cables were routed determined from the three trials used for normalization, underneath the riders’ clothing to a small backpack that where sEMG amplitude was averaged over a 5 s steady would house the Biometrics data logger. state isometric contraction for each trial. Subsequent on In the absence of a ground contact matt to synchronise course data for mean and peak sEMG are therefore the sEMG data for identifying the start of each run, run presented as a percentage of MVIC values (% MVIC). times were used and the raw sEMG data were cropped from the first change in elbow joint angle from the 0° Protocols

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Following determination of MVIC’s, riders performed 25.9 % MVIC, respectively; p=.008) and triceps brachii a 10 min self-paced warm up on a SRM indoor cycle and latissimus dorsi (22.0 ± 6.4 % MVIC; p=.031). No trainer, which included a series of short maximal effort significant differences were found for peak sEMG sprints. This was followed by self-selected dynamic between muscles within either MM or NT runs for DH stretching. Immediately prior to starting each run, the riders were instructed to remain static and to relax the upper body as much as possible to allow the setting of base line and zeroing the sEMG signals. Riders were then given the verbal command “3,2,1 GO” to start each run. Each rider performed one run of the MM and NT courses relevant to their respective discipline, preceded each time with the above warm up protocol and zeroing process. Chair-lifts were used to transport riders to the respective start points. The order of runs was randomised for all participants. Upon completion of each run data were transferred from the data logger for later analyses.

Statistical analyses A Shapiro-Wilk test determined that the data for Figure 1. Mean ± standard deviation of mean sEMG signal amplitudes as a percentage of maximal voluntary isometric contraction for DH riders during NT and each group were normally distributed. Differences MM downhill runs.¥ Significantly different to Triceps Brachii (MM); † Significantly between MM and NT courses were then analysed different to Triceps Brachii (NT). within groups using paired students t-tests. To determine whether differences existed between muscles by course, within groups one-way repeated measures ANOVA’s were used. To control for type I error the alpha levels were adjusted using a Bonferroni correction during post hoc analyses. If the homogeneity assumption was violated then the degrees of freedom were adjusted using the Greenhouse Geisser correction. Effect sizes were calculated using a partial Eta2 (η2). Significance was accepted at the p≤.05 level and data are presented as mean ± standard deviation values. All statistical procedures were conducted using SPSS 19.0 (SPSS Inc., Chicago, IL, USA).

Results Descriptive data for mean and peak velocity and Figure 2. Mean ± standard deviation of peak sEMG amplitudes as a percentage of run times are presented in table 1. maximal voluntary isometric contraction for DH riders during NT and MM downhill runs. Analysis of sEMG data revealed no significant differences (p>.05) in mean or peak values when expressed as a % MVIC, for any of the muscles when comparing activity between MM and NT courses for the DH riders. Mean sEMG data for each muscle, by course, are presented in figure 1, whilst figure 2 shows the peak sEMG data by course. When muscles were compared against each other within the MM runs, a significant difference was revealed in mean sEMG activity (F3,20 = 5.23, p=.008, η2 =.440). Post hoc analysis found mean differences between biceps brachii and triceps brachii (14.7 ± 7.1 and 46.4 ± 29.1 % MVIC, respectively; p=.016) and triceps brachii and latissimus dorsi (19.0 ± 6.3 % MVIC; p=.046).

Significant differences were also found for sEMG between muscles within the NT runs (F3,20 = 6.20, Figure 3. Mean ± standard deviation of mean sEMG amplitude as a percentage of p=.004, η2 =.480), with post hoc analysis showing maximal voluntary isometric contraction for XCO riders during NT and MM downhill the differences occurred again between biceps runs. ¥ Significantly different to Brachioradialis (MM); † Significantly different to Brachioradialis (NT). brachii and triceps brachii (16.9 ± 6.4 and 49.1 ±

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riders. Analysis of XCO riders’ sEMG data also revealed no significant differences in mean or peak sEMG between MM and NT courses (p>.05). Mean and peak sEMG values by course are presented in figures 3 and 4 respectively. When muscles were again compared against each other within courses, there was a significant difference in mean sEMG activity within MM runs (F3,20 = 3.77, p=.027, η2 =.361). Post hoc analysis revealed differences between biceps brachii and brachioradialis (13.8 ± 8.6 and 37.9 ± 15.8 % MVIC, respectively; p=.022). A significant difference was also found in mean sEMG amplitudes between muscles within the NT runs for the XCO riders (F3,20 = 4.25, p=.018, η2 =.389). Post hoc testing again found the differences to be between biceps brachii and Figure 4. Mean ± standard deviation of peak sEMG amplitude as a percentage of maximal voluntary isometric contraction for XCO riders during NT and MM downhill brachioradialis (12.1 ± 5.9 and 35.4 ± 18.0 % runs. MVIC, respectively; p=.013). No significant differences were found for peak sEMG amplitudes between muscles within either MM or NT runs for the XCO riders. No significant differences were found for mean elbow flexion angles within groups between NT and MM courses. Mean elbow flexion angles for each group are presented in figure 5.

Discussion To the best of our knowledge, this study represents the first to investigate the contribution of upper body musculature during field-based downhill MTB in elite athletes. A secondary aim was to determine the influence of course type on muscle activity in this population of elite XCO and DH cyclists. As data in this field of research is scare it Figure 5. Mean ± standard deviation of mean elbow joint angle for XCO and DH cyclists during man-made (MM) and natural terrain (NT) downhill mountain biking. is difficult to make direct comparisons to previous research. Furthermore, considering the differing length transmitted to the upper body muscles during a and nature of the courses used in the present study, it is simulated drop off. The ability of the bicycles to challenging to compare upper body muscle activity effectively absorb trail shock, likely also explains the between XCO and DH cyclists using statistical non-significant differences in sEMG within both analysis, though the discussion attempts to provide groups between MM and NT courses. some reasons for the apparent lack of differences in The riding dynamics of DH cyclists are different to upper body muscle activity. The key observations from those of XCO cyclists during descents. This may in part this investigation were: 1) when muscular activity were be due to DH bicycles having approximately 100 mm compared within groups, no differences were revealed more suspension travel than XCO bicycles and slacker between MM and NT courses for either XCO or DH bicycle frame head tube angles, thus influencing riding riders, 2) significant differences in mean sEMG dynamics. Such differences would potentially result in amplitudes were evident between muscles within both greater tyres contact with the ground, affording DH MM and NT courses for both XCO and DH groups and cyclists the ability to accelerate more frequently over 3) no significant differences in elbow joint angle rougher ground throughout the descents. This may have between courses within either group were revealed. led to the greater activity of the triceps brachii observed Though not directly tested for statistical comparisons in the present study in DH compared to XCO cyclists between groups due to the use of different course, as a result of increased lateral sways during sEMG amplitude would appear similar for both groups. acceleration. This theory is supported by Duc et al. The reduction in velocity seen in the XCO group and (2008) who also found that increases in lateral sways the technical differences in DH bicycle design and set when cycling uphill resulted in increased triceps brachii up may result in similar isolation of riders from trail activity. Further research is therefore warranted to shock, leading to comparable muscle activation determine the contribution of these lateral sways on between groups, with the exception of the triceps triceps brachii activity during downhill riding. brachii muscles. This supports the previous findings of Cross-country riders produced mean and peak Hurst at el. (2011) in that suspension reduces the forces velocities approximately 5 km.h-1 and 10 km.h-1 slower

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than DH riders on MM and NT courses, respectively. could also be due to the steeper courses, result in the These slower velocities may be imposed due to the greater engagement of the triceps brachii muscles in reduced suspension travel of XCO bicycles compared these DH riders, relative to the other tested muscles, as to DH bicycles used in the present study (100 ± 0 mm riders move body mass further towards the rear of the and 202 ± 1.55 mm, respectively). This difference may bicycle to maintain stability and control on steeper result in XCO riders reducing speed to maintain bike ground. Though not to a level of significance, the control, consequently reducing the number of muscle activity in the DH group was slightly lower accelerations and activity of the triceps brachii muscles. during MM runs than NT runs for all muscles Conversely, the longer travel DH bikes are capable of investigated. This possibly indicates a difference in absorbing much higher trail forces. In addition to body position due to the less steep gradient of the MM longer suspension travel, DH bicycles also have larger course, therefore reducing muscle activity and volume tyres run at lower pressures than those used for supporting the previous discussion point. In contrast, XCO, therefore further increasing ground contact the XCO group did not show any particular trend, as enabling higher velocities whilst still maintaining the activity of individual muscles different dependent control of the bike. upon which course was being ridden. This may be The higher speeds achieved by the DH riders are also reflective of differences in skill levels and competence likely in part to be the result of steeper DH courses, as in descending between riders in this group. However, evidenced by the greater vertical drop and descent both groups demonstrated high standard deviations for gradient outlined in the methods, and also the more all sEMG data extracted, which may be indicative of powerful brakes on DH bicycles, which allow riders to the wide variation in riding styles even within the brake later and therefore maintain speed more groups of elite riders tested in the current study. effectively. As the brakes are more powerful, DH riders Brachioradialis activity in both groups may be may also brake less frequently leading to the lower indicative of hand grip force on the handlebars and/or brachioradialis recruitment relative to triceps brachii braking. As stated previously, sensor placement on the muscles observed in the DH group, unlike that left side of the body was chosen as this was the side of observed in the XCO group. the front brake for all riders and the brake most used in Mountain bike suspension systems are set up largely cycling and as such would have potentially influenced based on rider body mass, with the compression and muscular activation. Though the magnitude of rebound rate of the shocks being adjusted to suit the activation was similar for both groups, the predominant type of course and terrain. As such, when these systems recruitment of the brachioradialis relative to other are set up for individual riders and courses this may upper body muscles in the XCO group may reflect result in an upper limit to force transmission to the these riders braking for longer during their descents muscles and for subsequent muscular activation, again than the DH riders. This may be due to the less leading to the seemingly comparable sEMG amplitudes powerful brakes fitted to XCO bicycles resulting in observed in each group. However, further investigation earlier and more prolonged braking. As discussed is warranted to identify the specific role suspension set previously, the brakes on DH bicycles are more up has on muscle activity. For this type of comparison powerful due to larger disc rotors and brake callipers. to be statistically valid, riders should perform over the This would potentially reduce the frequency and same course. However, this brings into question the duration of braking required for decelerating the ecological validity of such a study design and inherent bicycle. The use of accelerometers and brake levers risk to riders. instrumented with strain gauges may help determine Results also showed significant differences in mean the extent of the differences in braking frequency, sEMG amplitudes within groups over both courses braking force, and muscle activity between XCO and between muscles. Differences were observed in DH DH riders. riders during both MM and NT runs between biceps The finding that brachioradialis activity was the highest brachii and triceps brachii and triceps brachii and for the upper body muscles investigated for the XCO latissimus dorsi, with the triceps brachii producing the group in contrast the DH group may again reflect greatest % MVIC followed by the brachioradialis. In differences in body position on the bike. Modern XCO contrast, the XCO riders produced significant bicycles have a head tube angle of approximately 70- differences in mean sEMG amplitude between biceps 72º, compared to around 64-66º for DH bikes. This brachii and brachioradialis, with the latter being steeper angle would subsequently place XCO riders activated to the greatest extent, relative to the other into a more forward position and thus potentially upper body muscles investigated. These differences in resulting in more force being exerted on the muscle activity between groups most likely reflect brachioradialis. differences in riding styles and body position. Due to Peak sEMG values for both groups on both MM and the shorter travel bikes used in XCO racing, the XCO NT courses were greater than 100 % MVIC. This could riders in this study showed a trend for greater elbow be the result of several factors. Firstly, as a manual flexion, approximately 20º, over both courses than the resistance was used for the MVIC determination, it DH riders, presumably to aid the absorption of trail could be argued that true MVIC was not attained for shocks due to the reduced suspension travel available to each muscle. However, due to the field-based nature of them. The straighter elbow angle observed in DH riders the present study and according to the

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recommendations of Kendall et al (2005), the methods employ novel equipment that permits synchronisation used are justified. Alternatively, the peak sEMG values of GPS and sEMG data to extend upon the current observed during MTB descents may be due to the high study results. eccentric loads encountered by riders when landing from large drops and jumps. Though suspension Practical applications systems are effective in reducing these eccentric trail shocks, there is a limit to their capabilities and The findings of the current study appear to indicate therefore the riders themselves must also absorb some that course terrain has little influence on the mean of the trail shock with the upper body and leg muscles. and peak amplitudes of muscle activity during Future research may seek to use accelerometers to descent for both XCO and DH riders. However, there quantify the eccentric loading imposed on riders in are significant differences in activity between these specific instances. muscles of the upper body within courses in each group. The only true means of accurately comparing Limitations XCO and DH riders would be to have them ride the One of the limitations of the current study was the use same course. However, doing so would compromise of only one run per rider on each course. This was due the ecological validity of the study, as it is not to access constraints imposed by the ski resort realistic or safe to expect cyclists from different sub- operators. As such rider only had time to complete one disciplines of MTB to perform on courses they run on each course. Future research should endeavour would not normally encounter during racing. As such to perform multiple runs on different course to allow the findings of the current study provide a more means to be determined to account for the variability realistic representation into the demands of downhill often observed in sEMG measure. MTB descent in both elite XCO and DH bikers over Another potential limitation to the present study may be courses relative to their disciplines. the determination of mean and peak values over the The current findings also indicate that differences in whole runs. As riders completed their runs in different bicycle set ups and components may influence the times, muscular fatigue could potentially influence the physiological and biomechanical demands imposed mean and peak values determined. However, it should upon MTB riders during off road descending. be noted that at the time of testing, the ability to Athletes and coaches should therefore bear this in synchronise the sEMG and GPS data were not possible, mind when training and preparing for different races. making the use of techniques such as frequency Most elite cyclists participate in some form of analyses to quantify the contribution of fatigue muscular conditioning programme as part of their challenging. However, newer equipment now allows training. Given the current findings, XCO riders this synchronisation and would therefore enable the would potentially benefit from focusing on forearm evaluation of the impact of muscular fatigue on the strength as part of a general upper body conditioning current study results. Additionally, these systems would programme. In contrast, the present study would also allow researcher to accurately pinpoint muscle suggest that DH riders should prioritise the triceps activity at any given point on a course for all rider. brachii within their conditioning programmes due to Therefore, any future investigations should seek to the increased recruitment of this muscle group during employ these newer systems. downhill riding that was observed. Increases in strength, particularly in these areas may result in Conclusions lower sEMG activity for a given force, therefore In conclusion, this study revealed differences between potentially reducing muscle fatigue and the risk of upper body muscles in mean and peak activity in elite injury and improving overall performance. XCO and DH mountain bike riders, though the magnitude of activation differed little between groups Acknowledgment irrespective of riding conditions. This may be due to We gratefully acknowledge the Swedish Olympic Committee differences in riding dynamics and bicycle set-up. for funding this project and the Swedish Winter Sports Research Centre and Åre Bike Park for their assistance in Future research could aim to quantify the impact of data collection. We would also like to thanks all the athletes suspension set-up on muscle activity and investigate involved in the research project for their time and effort. hand grip and braking forces and their influence on muscular fatigue during downhill MTB. The use of a References standardised course would help evaluate the impact of 1. Blake, OM., Champoux, Y. and Wakeling, JM. (2012) these systems on the physiological and biomechanical Muscle Coordination Patterns for Efficient Cycling. demands of off road descending and allow direct Medicine and Science in Sports and Exercise, 44(5), comparisons to be made between XCO and DH riders, 926-938. though such a study design would lack the ecological 2. Duc, S., Bertucci, W., Pernin, J.N. and Grappe, F. validity of the current study alluded to previously. (2008) Muscular activity during uphill cycling: Effect of slope, posture, hand grip position and constrained Despite the limitations, the present study still presents bicycle lateral sways. Journal of Electromyography and the first investigation to attempt to evaluate the upper Kinesiology, 18, 116-127. body muscle contribution to performance in off road 3. Egaña, M., Ryan, K. and Warmington, SA., and Green, downhill MTB and to determine the influence of course S. (2010) Effect of body tilt angle on fatigue and EMG type on muscle activity. Future research should seek to

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activities in lower limbs during cycling. European Journal of Applied Physiology. 108, 649–656. 4. Freeman, S., Karpowicz, A., Gray, J. and McGill, S. (2006) Quantifying muscle patterns and spine load during various forms of the push up. Medicine and Science in Sports and Exercise, 38(3), 570-577. 5. Hurst, H.T. and Atkins, S. (2006) Power output of field- based downhill mountain biking. Journal of Sports Sciences, 24(10), 1047-1053. 6. Hurst, H.T., Sinclair, J., Edmundson, C.J., Brooks, D. and Mellor, P.J. (2011) The effect of suspension forks on upper body muscle activation during a simulated mountain bike drop-off. Proceedings of the 16th Annual Congress of the European College of Sports Sciences, (Liverpool, July), p455. 7. Impellizzeri FM, Rampinini E, Sassi A, Mognoni, P. and Marcora, S. (2005) Physiological correlates to off- road cycling performance. Journal of Sports Sciences, 23, 41-47. 8. Jackson, A.S. and Pollock, M.L. (1978) Generalized equations for predicting body density of men. British Journal of Nutrition, 40, 497-504. 9. Kendall, F.P., McCreary, E.K., Provance, P.G., Rodgers, M.M., Romani, W.A. (2005) Muscles testing and function with posture and pain (5th Edition). Lippincott Williams and Wilkins, UK. 10. Lee, H., Martin, D.T., Anson, J.M., Grundy, D. and Hahn, A.G. (2002) Physiological characteristics of successful mountain bikers and professional road cyclists. Journal of Sports Sciences, 20, 1001-1008. 11. Li and Caldwell G.E. (1998). Muscular coordination in cycling: effect of surface incline and posture. Journal of Applied Physiology, 85, 927–934. 12. Li and Caldwell G.E. (1999). Coefficient of cross correlation and the time domain correspondence, Journal of Electromyography and Kinesiology, 9, 385– 389. 13. Lohman, T.G., Roche, A. and Martorell, R. (1989) Anthropometric Standardisation Reference Manual. Leeds, Human Kinetics. 14. Matsuura, R., Arimitsu, T., Yuncki, T. and Yuno, T. (2011) Effects of resistive load on performance and surface EMG activity during repeated cycling sprints on a non-isokinetic cycle ergometer. British Journal of Sports Medicine. 45(10), 820-824. 15. Prins, L., Terblanche, E. and Myburgh, KH. (2007) Field and laboratory correlates of performance in competitive cross-country mountain bikers. Journal of Sports Sciences, 25(8), 927 – 935. 16. Sperlich, B., Achtzehn, S., Buhr, M., Zinner, C., Zelle, S. and Holmberg, H-C. (2012) Salivary cortisol, heart rate, and blood lactate responses during elite downhill mountain bike racing. International Journal of Sports Physiology and Performance, 7(1), 47 – 52. 17. Stapelfeldt, B., Schwirtz, A., Schumacher, Y.O. and Hillebrecht, M. (2004) Workload demands in mountain bike racing. International Journal of Sports Medicine, 25, 294-300. 18. Union Cycliste Internationale (2012) UCI cycling regulations: Part IV Mountain Bike Races. Union Cycliste Internationale, Switzerland, 1-68. 19. Wilber, R.L., Zawadzki, K.M., Kearney, J.T., Shannon, M.P. and Disalvo, D. (1997) Physiological Profile of Elite Off-Road and Road Cyclists. Medicine and Science in Sports and Exercise, Vol. 29(8), 1090-1094.

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